Question

Phenyl isocyanide test is used to identify:
A. aromatic secondary amines
B. aromatic tertiary amines
C. aromatic primary amines
D. quaternary ammonium compounds

Answer 1

Hint: The phenyl isocyanide test is also known as the carbylamine test in which there is a synthesis of an isocyanide with the help of a reaction between chloroform, primary amine and a base. The reaction consists of an intermediate, dichlorocarbene.

Complete step by step answer:
As the carbylamine reaction is only effective for primary amines, it can be used as a chemical test for the presence of primary amines. In this context, the reaction is also called as the Saytzeff's isocyanide test. In this reaction, the unknown substance is heated up with alcoholic potassium hydroxide and chloroform. If a primary amine is present, the isocyanide (carbylamine) is formed which is indicated by a foul smell. The carbylamine test gives a negative reaction with secondary and tertiary amines.
The mechanism of the reaction involves an addition of an amine group to the dichlorocarbene which is simply formed by the removal of a chlorine atom and a hydrogen atom (overall termed as dehydrohalogenation). This dichlorocarbene acts as a Lewis acid and receives electrons from the nitrogen atom of the primary amine group. Later there are two base mediated dehydrochlorination reactions which lead to the formation of isocyanide.
Thus, the correct option is C. aromatic primary amines.

Thus, the correct option is C. aromatic primary amines.

Note:
Whenever different samples containing a primary, secondary, tertiary or quaternary amine group is been given for identification, the easiest way to differentiate a primary amine is the application of the phenyl isocyanide test which does not occur in others.